<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  #i1 {
    color: red;

  }

  .c1 {
    color: green !important;
  }

  .c2 {
    background-color: aqua;
  }

  .c1.c2.c3.c4.c5.c6.c7.c8.c9.c10.c11 {
    color: yellow;
  }
</style>

<body>
  <div id="i1" class="c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11">123456</div>
</body>

</html>